1. Field of the Invention
The present invention relates to an integrated active-matrix liquid-crystal display device in which driver circuits and other peripheral circuits are formed on the same substrate as the pixel elements, and more particularly to a liquid-crystal display device equipped with a checkout circuit for detecting driver circuit malfunctions, break or short of data bus lines or scanning bus lines, and other failures.
2. Description of the Related Art
In an active-matrix-type liquid-crystal display device, each pixel electrode has a selection transistor, and scanning buses are energized to cause the selection transistor to conduct. A picture that corresponds to video signals is displayed by applying video signals on a data bus to pixel electrodes via the selection transistors. Thin-film transistors are therefore formed in matrix on glass and other transparent substrate surfaces.
It has been common in the past to use LSI circuits to separately form driver circuits for driving the aforementioned scanning buses or data buses and to mount the driver circuits on motherboards or the like. The modular boards of such driver circuits are connected by cables or the like to the bus lines on display substrates.
In recent years, however, it has been proposed to cut costs by forming not only the transistors of pixel areas but also driver circuits and other peripheral circuits on the same substrate. In such integrated active-matrix liquid-crystal display devices, peripheral circuits are composed of thin-film transistors in the same manner as the transistors of pixel elements. Costs are expected to be lowered by manufacturing the transistors of peripheral circuits together with the transistors of the pixel areas.
In the past, only those LSI circuits that had been found to have satisfactory quality as a result of an inspection process could be used in driver circuits and other peripheral circuits composed of individual LSI circuits. In an integrated display device, however, peripheral circuits are formed together with the pixel area on a transparent substrate, making it impossible to determine in advance whether these driver circuits or the like will operate properly.
In addition, a liquid-crystal display device is assembled by injecting liquid crystals between a panel in which a pixel electrode is formed and a panel in which a common electrode is formed. Faulty panels should therefore be removed as a result of an inspection process that precedes the assembly stage. If defects are discovered after a device has been completed, the entire finished product must be discarded, reducing the production yield and driving up overall costs.
An integrated active-matrix-type liquid-crystal display device has been proposed in recent years, but a technique for optimizing the performance check of integrally formed driver circuits has yet to be proposed.